1. Field of the Invention
The present invention relates to a semiconductor device including a memory and having capability of performing wireless communication. In addition, the present invention relates to a driving method of the semiconductor device to determine timing of writing data into the memory.
2. Description of the Related Art
With development in computer technology, technology for information identification without contact has been a practical use and a memory performing a stable operation without contact has been needed. In response to such a demand, a wireless tag capable of communication without contact has been developed recently.
Some wireless tags include a function of memories. The memories, for example, can store data specific to the wireless tags, and data of programs for operating integrated circuits inside the wireless tags.
The wavelength of a radio wave transmitted and received between wireless tags and reader/writers, which are called interrogators, includes 125 kHz, 13.56 MHz, 915 MHz, 2.45 GHz, and the like. Each of the wavelength is standardized by ISO or the like. In addition, methods for modulation and demodulation in transmitting and receiving are standardized.
Wireless tags capable of generating electric power as a power supply voltage for operating the wireless tags from a radio wave also use the electric power which is generated from a radio wave in storing data into a memory. Normally, for storing data into the memory, a voltage which is obtained from a radio wave is utilized after being boosted up in the wireless tags.
For example, according to Patent Document 1 (Japanese Published Patent Application No. 2006-293690), when data is written into a memory, a voltage supplied to the memory is changed from 3.3V into 12.0 V, which is a higher voltage.